1. Field of the Invention
The present invention relates to a multi-nozzle inkjet recording apparatus capable of high-speed printing.
2. Description of the Background Art
Inkjet printing has come to be widely used in digitally controlled printing apparatuses due to certain advantages, such as, for example, reduced shock, low noise, and system simplicity. In light of the advantages of the inkjet printing method, many types of inkjet recording apparatuses have been developed and are now commercially available for various purposes, ranging from home use to office use and business use.
The inkjet printing used in color image printing apparatus employs two types of jetting technologies: drop-on demand (DOD) type and continuous inkjet type. In both jetting technologies, a plurality of color inks may be used for forming color images, in which ink of each color is supplied to a print head through separate ink supply paths. The print head includes nozzles from which ink droplets are selectively jetted, and the jetted ink droplets strike a recording medium to form an image thereon. In both cases, a separate ink supply system must be provided for each color of ink used for image forming operations such as printing. Typically, subtractive colors (i.e., cyan, yellow, magenta) are used because these three primary colors can be combined to generate several million recognizable colors.
In inkjet printing using the DOD technique described above, a pressure generating actuator such as a piezoelectric element, or a heating member such as heater, is employed to generate ink droplets directed onto a recording medium. Examples of such methods are described in U.S. Pat. Nos. 3,683,212, 3,747,120, 3,946,398, and 4,723,129. A method of using the heating member, which may be referred to as a thermal inkjet method or bubble jet (registered trademark), is one in which gas is heated to expand and form bubbles of ink that form ink droplets. By activating a piezoelectric actuator or a heater selectively, the ink droplets can be formed and jetted from the print head. The jetted ink droplets travel or fly through a space between the print head and a recording medium and strike the recording medium. An image can be formed on the recording medium by changing a relative position of the print head and the recording medium and controlling the pattern of ejected ink droplets.
By contrast, in continuous inkjet printing, a continuous stream composed of ink droplets is generated by using a pressurized ink supply. A conventional continuous inkjet recording apparatus may use an electrostatic charging device as described in U.S. Pat. No. 3,373,437 to generate a continuous stream of ink droplets. The electrostatic charging device may be disposed at a position near to a leading edge of a filament-like column of ink, in which ink droplets are formed by separating ink from the leading edge of the ink column, and the separated ink droplet is charged by the electrostatic charging device, and then guided to a given position or in a given direction using a deflection electrode having a large potential difference. When no image forming operation such as printing is being performed, ink droplets may be deflected into and recovered by an ink catching unit (e.g., gutter), and such recovered ink may be re-used or discarded. An image forming operation, when it is performed, may be conducted as follows: In one case, when an image forming operation such as printing is performed, ink droplets, which are not deflected, are directed onto a recording medium; alternatively, deflected ink droplets may be directed onto a recording medium while un-deflected ink droplets are collected or recovered by an ink catching unit.
Such continuous inkjet recording apparatuses using an electrostatic charging/deflection mechanism can perform an image forming operation faster and provide better quality images than a drop-on demand (DOD) type apparatus. However, the electrostatic charging/deflection mechanism generally costs more to manufacture and tends to malfunction more often.
In light of such situation, another type of continuous inkjet recording apparatus or system has been proposed as described in U.S. Pat. No. 7,413,293, for example. In such system, a weak heat pulse is applied to an ink column jetted from a nozzle cyclically or periodically using a heater to form separated ink droplets, which are ink droplets separated from the ink column. As such, ink droplets can be formed at a given position distanced from the nozzle by applying a heat pulse at a given timing. The ink droplets can be further categorized as deflected ink droplets and un-deflected ink droplets (or straightforward ink droplets). Both the deflected ink droplets and un-deflected ink droplets can be formed by changing the pattern in which the heat pulses are applied to the ink droplets at a position near to a nozzle exit using the heater. For example, heat pulses may be applied to the ink asymmetrically.
Then, in one configuration, when the deflected ink droplets are traveling in one direction, a flow of gas in a given direction causes the deflected ink droplets to change direction. The deflected ink droplets may be caught by a recovery unit while the un-deflected ink droplets strike a recording medium to form an image thereon.
Conversely, in another configuration, when the un-deflected ink droplets are traveling in one direction, a flow of gas in a given direction causes the un-deflected ink droplets change direction. In this case, the un-deflected ink droplets are caught by a recovery unit while the deflected ink droplets strike a recording medium to form an image thereon.
Such continuous inkjet recording apparatuses using a gas flow do not need to use a conventional electrostatic charging/deflection mechanism, and thereby can enhance ink droplet control. Further, because the electrostatic charging/deflection mechanism can be omitted, a nozzle arrangement density in the continuous inkjet recording apparatus can be increased to, for example, 600 to 2400 dots per inch (dpi). Accordingly, the inkjet head can be provided with more nozzles to match the entire width of the recording medium. Such multi-nozzle inkjet head may be fixed at a given position, and the recording medium may be transported in one direction under the inkjet head for high-speed printing, for example.
However, such an apparatus or system has not been examined extensively for its reliable performance such as stable ink droplet formation, ink jetting, and ink travel because of its employment of the multi-nozzle ink jetting having a greater number of nozzles.